Telephone circuits and method of operating the same



Jana 8, 1924. 1,480,210

K. s. JOHNSON TELEPHONE CIRCUITS AND METHOD OF OPEI YATING THE SAME Filed Sept. 5, 1919 fiwe/vfor; Ken/791% J? Johnson b M An) Patented Jan. 8, 1924.

UNITED STATES PATENT OFFICE.

KENNETH S. JOHNSON, OF JERSEY CITY, NEW JERSEY, ASSIGNOR T WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE CIRCUITS AND METHOD OF OPERATING THE SAME.

Application filed September 5, 1919. Serial No. 821,890.

To all whom it may concern.

Be it known that I, KENNETH S. JOHNSON, a citizen of the United States, residing at Jersey City, in the county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Telephone Oircuits and Methods of Operating the Same, of which the followin is a full, clear, concise, and exact description.

This invention relates to telephone circuits and more particularly to circuits having a branch through which it is desirable at times to prevent the passage of talking currents, as-

for example, to render a substation circuit anti-side-tone.

It is the object of the invention to provide a method and means for preventing the passage of talking currents through one branch of a circuit of the above type, when the portion of the circuit adjacent said branch is employed for transmitting currents to another portion of the circuit, but permitting the passa e of currents through said branch when suc currents are received from another source of currents.

In the embodiment of the invention disclosed herein, a two-button transmitter is employed in a circuit having three branches, i. e., a circuit comprising three electric paths between two common terminals. One of these branches comprises a telephone line, one comprises a receiver, and one comprises a balancing impedance which in two of the forms of the invention shown is partially or wholly incorporated in one button of said transmitter. The relation of impedances and the direction of electromotive forces generated in the transmitter buttons are such that, on transmitting, substantially no talking current flows through the receiver.

While the invention is shown applied to substation circuits, it is obvious that it is applicable to other circuits where it is desired to transmit variable currents without actuating an electrical device in one branch of the circuit.

Furthermore, it is obvious that other types of transmitters, such as the electromagnetic or electrostatic types, may be employed instead of the carbon button type. In

the appended claims, the expression twoelement transmitter is intended to mean a transmitter having two elements, each of which is capable of generating a variable electromotive force in response to mechanical vibrations.

The invention will be more fully understood from the following detailed description and claims taken in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic view of one form of the invention; Fig. 2,is a similar view showing the direction of currents in Fig. 1, when transmitting, and showing the balancing impedance as separate from the transmitter;

- Fig. 3 represents another form of the invention; Fig. 4 shows the direction of currents in Fig. 3 when transmitting; Fig. 5 represents a third form of the invention; Fig. 6 shows the direction of currents in Fig. 5, when transmitting and shows the balancing impedance as separate from the transmitter; Fig. 7 represents diagrammatically a transmitter which may be used in the circuits of Fig. 1 or of Fig. 5; and Fig. 8 is a similar View of, a transmitter which may be used in the circuit of Fig. 3.

In Figs. 2, 4 and 6 the portions of the circuit through which current variations do not flow are shown in dotted lines.

Referring to Fig. 1, the circuit may be considered to consist of three. branches 10, 11 and 12. The branch 10 comprises the line L and one button T of a two button transmitter. The branch 11 comprises the receiver R and the branch 12 comprises the other transmitter button T The button T is preferably designed to have an impedance which will properly balance the impedance of the line and render the substation antiside tone. Additional impedance may, however, be inserted in series in branch 12 as indicated at X in Fig. 2. The source of direct current is not shown, since it will ordinarily be located at a central station.

that on transmitting, the electromotive forces enerated therein aid each other in the series circuit comprising branches ,10 and 12. The values of these electromotive forces are such that equal potential variations occur at the receiver terminals and substantially no variable current flows through the receiver. Assuming that the electromotive force in a transmitter button is proportional to the s uare root of its impedance, the following impedance relations must exist for no side tone:

T,=T,+2L+ 1 3 In equation (1) '1 and T and L represent the impedances respectively of the elements above designated by these characters. This formula is derived as follows:

Let the electromotive force generated in the button T be represented by KJT, and the electromotive force in T by Km Since it is assumed that there is no current in R, the current flows serially through the line and the two transmitter buttons. Designating this current by I, then by Ohms law KJ'ITFIL 3 Substituting the value of T from equation (2) in equation (3), we get:

Solving this equation for the value of T we obtain equation (1) given above.

If the transmitter buttons in the circuit of Fig. 1 are in conductive relation to the diaphragm, the transmitter may be of the type shown schematically in Fig. 7, wherein the W0 buttons are arranged to be compressed simultaneously by the diaphragm. The push-pull transmitter shown in Fig. 8 may be used if the direct current is made to flow through the buttons in parallel.

In Figs. 3 and 4 the receiver is placed in the branch 12 and the balancing impedance X in the branch 11. To insure no side tone in this form the electromotive forces generated in the transmitter buttons must be opposed and the change in electromotive force in button T must be equal to the change in potential drop through impedance X.

The circuit of Figs. 5 and 6 is similar to that of Fig. 3, except that the balancing immasonic included in transmitter button T The form of transmitter represented in Fig. 8 may be used in Figs. 3 and 4. The arrangement is such that one button is compressed when the other is expanded, thus producing opposite potential variations when the direct current is flowing through the buttons in series. In Figs. 5 and 6, when current supplied by a central battery flows through the buttons in parallel, the transmitter of Fig. 7 may be used.

-What is claimed is:

1. A circuit comprising three branches, a device for converting sound waves into electric waves in each of two of said branches, and means for simultaneously actuating said devices, the electromotive forces generated by said actuation being so proportioned that substantially no current variations will flow in one of said branches, a receiver in said last mentioned branch and a line circuit included in one of. the others of said branches.

2. A circuit comprising three branches, a receiver in one of said branches, a device for converting sound waves into electric wavesin each of two of said branches, and means for simultaneously actuating said devices, the electromotive forces generated by said actuation being so proportioned that substantially nocurrent variations will flow in said receiver.

3. A. circuit comprising three branches, a device for converting sound waves into electric waves in each of two of said branches, a receiver in the third of said branches, and

, means for simultaneously actuating said devices, the electromotive forces generated by said actuation being so proportioned that substantially no current variations will flow in said receiver.

45. The method of operating a threebranched telephone circuit, which comprises converting sound waves into alternating electromotive forces in each of two of said branches of such values that substantially no current flows in one of said branches.

5. The method of operating a threebranched telephone circuit, which comprises converting sound waves into alternating electromotive forces in each of two of said branches of such values that substantially no current flows in the third of said branches,

6. A telephone circuit comprising a line, and two branches connected to said line, a two-element transmitter having one element in said line and one element in one of said branches, and a receiver in one of said branches, the impedances of said elements being so proportioned to each other and to the impedances of the lineand of the branch not containing the receiver that said receiver is substantially anti-side tone.

7. A telephone circuit comprising a line, and two branches connected to said line, a two'element transmitter having one element in said line and one element in one of said branches, and a receiver in the other of said branches, the impedance of said elements being so proportioned to each other and to the line impedances of the line and of the first of said branches that said receiver is substantially anti-side-tone.

8. In combination, a line, a two-element transmitter connected to said line, a receiver in a branch in shunt to one of said elements, and means for actuating said elements to produce talking currents in series there-; through, the impedance of said shunted element being so proportioned to the impedances of the other element and of the line that the terminals of said receiver are subjected to substantially the same potential variations during said actuation.

9. In combination, a line, a transmitter comprising a diaphragm and two buttons in contact with one face thereof, opposite sides of said line being connected to said buttons respectively,-and a receiver having one terminal connected to said diaphragm and one terminal connected to said line.

10. In a telephone circuit, two devices for converting sound waves into electric waves, and a receiver so connected thereto that when said devices are simultaneously actuated by a sound wave substantially no current will flow in said receiver.

11. In a telephone circuit, two devices for converting sound waves into electric waves,

and a receiver connected thereto, said desaid electromotive forces substantially ba1- ance each other in said receiver.

In witness whereof, I hereunto subscribe my name this 2nd day of September A. D.,

KENNETH S. JOHNSON. 

